Mabey has announced details on its involvement in the construction of two new low-head hydro power stations in Yorkshire, developed by Barn Energy and built by Eric Wright Civil Engineering.

Commissioned in August 2016, the Kirkthorpe hydro power station, on the river Calder near Wakefield, Yorkshire, is sited alongside the weir that generates the drop in water levels. The turbine and generating equipment are built into a horseshoe channel that routes water from above the weir and back into the main flow channel. Mabey worked with the principal stakeholders to build a 10.5m deep cofferdam with proprietary props and struts supporting the structure. The horseshoe shaped excavation required extensive angled propping and shear connections, along with ground reduction and tie back anchors to create the composite temporary works design.

Mabey's involvement in the Kirkthorpe project has lasted for 12 months, with its expertise being called upon several times to provide input and develop further solutions as the site developed and plans were modified. Its involvement in the Kirkthorpe project was requested by Eric Wright, following its contributions to the Thrybergh hydro power project last year.

The Thrybergh hydro power station was commissioned at the end of 2015. The weir creating the level drop required is located at an existing bend in the river, and the hydro project was constructed in a regular rectangular shaped cofferdam, cutting the corner on the bend to take advantage of the head drop across the weir. It required excavations 7m deep adjacent to, and within, the river.

During the planning stages for the Thrybergh station, Mabey recommended using heavier than necessary sheet piles for the cofferdam excavation, in order to reduce the amount of props and beams required. This allowed Eric Wright to reduce the number of sequences needed to complete the project, provide greater room for manoeuvre within the excavation, and save on the cost of hire equipment. Since completion, the 260kW power station has achieved its target generation figure of 1000MWh three months earlier than planned.

 Gavin Hulme, contracts manager, Eric Wright Civil Engineering, said, “[We] have worked together with Mabey on two hydro-electric schemes to date and we have found their input invaluable in helping us to deliver these projects successfully. At all times Mabey has been proactive and flexible in repeatedly revisiting their designs to explore all options and ensure we obtained best value”.

To view HD aerial video footage, taken at several points during the excavation and construction, click here.

Above: An aerial shot showing the cofferdam excavation at Kirkthorpe, supported by Mabey's proprietary struts and beams.